Usually when a battery is pulled all the way down, They don't come back.
you should try slow recharge. It might work. I have found that when car
batteries are pulled down to about 10v 3 times, they become worthless.
Good Luck
Frank

Veggie wrote:

I have a car with a battery that is completely discharged (accessory
left on for over 24 hours). Read 0 volts.

What is the best way to remedy this?

a) jump start - it seems to not be a good option as it dumps high
current into the dead battery. If you're on the road somewhere, sure,
you need to get going but jump starting seems to be undesirable.

b) put it on a battery charger, one of those 5/10/25 amp ones. If so,
which rate is the best for a completely flat battery?

There seems to be a lot said about sulfate build up on batteries. It
seems to be an unsettled subject on the Net, as many say one thing but
an equal number refute it. One claim in interesting to me- that
leaving a lead acid battery in flat condition for a long time caused
sulfate build up. Is this true, and what is a "long time"? Are we
talking days, weeks, or months?